This invention describes a method for enlarging cell sizes of alkenyl aromatic foams by blending polymers which comprise; (A) alkenyl aromatic polymers, and (B) vinyl or vinylidene aromatic and/or sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene substantially random interpolymers. Suitable alkenyl aromatic polymers include alkenyl aromatic homopolymers and copolymers of alkenyl aromatic compounds and copolymerizable ethylenically unsaturated comonomers. The alkenyl aromatic polymer material comprises greater than 50 and preferably greater than 70 weight percent alkenyl aromatic monomeric units. Most preferably, the alkenyl aromatic polymer material is comprised entirely of alkenyl aromatic monomeric units. Suitable alkenyl aromatic polymers include those derived from alkenyl aromatic compounds such as styrene, alpha-methylstyrene, etc. A preferred alkenyl aromatic polymer is polystyrene. Examples of copolymerizable compounds include acrylic acid, methacrylic acid, acrylonitrile, etc. The substantially random interpolymers comprise polymer units derived from ethylene and/or one or more xcex1-olefin monomers with specific amounts of one or more vinyl or vinylidene aromatic monomers and/or sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers. A preferred substantially random interpolymer is an ethylene/styrene interpolymer. Incorporation of the substantially random interpolymer in the blend with the alkenyl aromatic polymer allows the formation of foams having enlarged cell sizes when blowing agents of reduced or zero ozone-depletion potential (which have low solubility and relatively high nucleation potential) are employed.
Due to present environmental concerns over the use of ozone-depleting blowing agents, it is desirable to make alkenyl aromatic polymer foams with blowing agents having reduced or zero ozone-depletion potential. Such blowing agents include inorganic blowing agents such as nitrogen, sulfur hexafluoride (SF6), and argon; organic blowing agents such as carbon dioxide and hydrofluorocarbons such as 1,1,1,2-tetrafluoroethane (HFC-134a), 1,1,2,2-tetrafluoroethane (HFC-134), 1,1,1,3,3-pentafluoropropane, difluoromethane (HFC-32), 1,1-difluoroethane (HFC-152a), pentafluoroethane (HFC-125), fluoroethane (HFC-161) and 1,1,1-trifluoroethane (HFC-143a) and hydrocarbons such as methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane, cyclopentane and neopentane; and chemical blowing agents which include azodicarbonamide, azodiisobutyro-nitrile, benzenesulfonylhydrazide, 4,4-oxybenzene sulfonyl-semicarbazide, p-toluene sulfonyl semi-carbazide, barium azodicarboxylate, N,Nxe2x80x2-dimethyl-N,Nxe2x80x2-dinitrosoterephthalamide, trihydrazino triazine and mixtures of citric acid and sodium bicarbonate such as the various products sold under the name Hydrocerol(trademark) (a product and trademark of Boehringer Ingelheim). All of these blowing agents may be used as single components or any mixture in combination thereof, or in mixtures with other co-blowing agents.
A problem with using the above non ozone-depleting blowing agents is their tendency to form foams of relatively small cell size and cross-section. Such blowing agents typically result in foams having small cell sizes due to their relatively high nucleation potential. Small cell size is especially a problem when particular infrared attenuating agents are employed such as carbon black, graphite, and titanium dioxide.
It would be desirable to be able to employ the non-ozone depleting blowing agents in making alkenyl aromatic polymer foams with or without infrared attenuating agents yet be able to enlarge the cell size of the foam. Enlarging the cell size of the foams would enable greater thicknesses and larger cross-sectional areas to be obtained, as well as afford a reduction in foam density in some cases. Lower foam densities would be desirable for both extruded and expanded alkenyl aromatic polymer foams. Greater foam thicknesses and cross-sections would enable a broader range of products to be manufactured, and reducing density would allow foams to be manufactured more economically. It is also desirable for the foams to exhibit acceptable physical properties.
Prior art attempts to make a foam having enlarged cell size include the integration of a wax in a foam forming gel prior to extrusion of the gel through a die to form a foam. Such use of a wax is seen in U.S. Pat. No. 4,229,396, which is incorporated herein by reference. The use of a wax may however, present processing problems and cause thermal stability variations or diminution in physical properties in product foams. The wax may also cause inconsistency in extrusion temperatures. Additional prior art attempts to make a foam having enlarged cell size include the incorporation of a non-waxy compound in a foam forming gel prior to extrusion of the gel through a die to form a foam. Such use of a non-waxy compound is seen in U.S. Pat. No. 5,489,407, which is incorporated herein by reference. Large cell size alkenyl aromatic polymer foams have been prepared using glycerol monoesters of C8-C24 fatty acids as cell size enlarging agents as disclosed in U.S. Pat. No. 5,776,389, the entire contents of which are incorporated herein by reference. However the concentration of such agents in a foam that can be used is limited, as high levels depress the glass transition temperature of the polymer and can result in degradation of physical properties such as creep under load (at 80xc2x0 C.).
Thus it would be desirable to identify cell size enlarging compounds which can be used in conjunction with non-ozone depleting blowing agents and do not have an adverse effect on the physical or mechanical properties of the foam.
The present invention pertains to improved closed cell alkenyl aromatic polymer foams having enlarged cell size, comprising;
(A) from about 80 to about 99.7 percent by weight (based on the combined weight of Components A and B) of one or more alkenyl aromatic polymers, and wherein at least one of said alkenyl aromatic polymers has a molecular weight (Mw) of from about 100,000 to about 500,000; and
(B) from about 0.3 to about 20 percent by weight (based on the combined weight of Components A and B) of one or more substantially random interpolymers having an I2 of about 0.01 to about 1000 g/10 min, and an Mw/Mn of about 1.5 to about 20; comprising;
(1) from about 8 to about 65 mol % of polymer units derived from;
(a) at least one vinyl or vinylidene aromatic monomer, or
(b) at least one hindered aliphatic or cycloaliphatic vinyl or vinylidene monomer, or
(c) a combination of at least one aromatic vinyl or vinylidene monomer and at least one hindered aliphatic or cycloaliphatic vinyl or vinylidene monomer, and
(2) from about 35 to about 92 mol % of polymer units derived from at least one of ethylene and/or a C3-20 xcex1-olefin; and
(3) from 0 to about 20 mol % of polymer units derived from one or more of ethylenically unsaturated polymerizable monomers other than those derived from (1) and (2); and
(C) optionally, one or more nucleating agents and
(D) optionally, one or more other additives; and
(E) one or more blowing agents having zero ozone depletion potential and, optionally one or more co-blowing agents, present in a total amount of from about 0.2 to about 5.0 g moles per kg (based on the combined weight of Components A and B); wherein
the cell size of said foam is enlarged about 5 percent or more relative to a
corresponding foam without the substantially random interpolymer.
This combination allows the manufacture of low density alkenyl aromatic polymer foams of enlarged cell size and relatively thick cross-section, when blowing agents of relatively high nucleation potential are employed. When these blowing agents are used with alkenyl aromatic polymer in the absence of the substantially random interpolymers, small cell foams result. In addition, we have unexpectedly found that cell size can be enlarged by using substantially random interpolymers without a substantial degradation of foam mechanical properties (as occurs if high concentrations of prior art cell size enlargers such as glycerol monoesters are used). Furthermore foam density can be decreased in some cases, which is desirable for both extruded and expanded foams made from alkenyl aromatic polymers.
Definitions
All references herein to elements or metals belonging to a certain Group refer to the Periodic Table of the Elements published and copyrighted by CRC Press, Inc., 1989. Also any reference to the Group or Groups shall be to the Group or Groups as reflected in this Periodic Table of the Elements using the IUPAC system for numbering groups.
Any numerical values recited herein include all values from the lower value to the upper value in increments of one unit provided that there is a separation of at least 2 units between any lower value and any higher value. As an example, if it is stated that the amount of a component or a value of a process variable such as, for example, temperature, pressure, time and the like is, for example, from 1 to 90, preferably from 20 to 80, more preferably from 30 to 70, it is intended that values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 etc. are expressly enumerated in this specification. For values which are less than one, one unit is considered to be 0.0001, 0.001, 0.01 or 0.1 as appropriate. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.
The term xe2x80x9chydrocarbylxe2x80x9d as employed herein means any aliphatic, cycloaliphatic, aromatic, aryl substituted aliphatic, aryl substituted cycloaliphatic, aliphatic substituted aromatic, or aliphatic substituted cycloaliphatic groups.
The term xe2x80x9chydrocarbyloxyxe2x80x9d means a hydrocarbyl group having an oxygen linkage between it and the carbon atom to which it is attached.
The term xe2x80x9ccopolymerxe2x80x9d as employed herein means a polymer wherein at least two different monomers are polymerized to form the copolymer.
The term xe2x80x9cinterpolymerxe2x80x9d is used herein to indicate a polymer wherein at least two different monomers are polymerized to make the interpolymer. This includes copolymers, terpolymers, etc.
The term xe2x80x9cenlarged cell sizexe2x80x9d is used herein to indicate a foam having an increase of cell size of about 5%, preferably about 10%, more preferably about 15% or more relative to an analogous foam made without the substantially random interpolymer.
The invention especially covers foams comprising blends of one or more alkenyl aromatic homopolymers, or copolymers of alkenyl aromatic monomers, and/or copolymers of alkenyl aromatic monomers with one or more copolymerizeable ethylenically unsaturated comonomers (other than ethylene or linear C3-C12 xcex1-olefins) with at least one substantially random interpolymer. The foams of this invention have enlarged cell sizes relative to corresponding foams of similar density made without the substantially random interpolymer.
The alkenyl aromatic polymer material may further include minor proportions of non-alkenyl aromatic polymers. The alkenyl aromatic polymer material may be comprised solely of one or more alkenyl aromatic homopolymers, one or more alkenyl aromatic copolymers, a blend of one or more of each of alkenyl aromatic homopolymers and copolymers, or blends of any of the foregoing with a non-alkenyl aromatic polymer. Regardless of composition, the alkenyl aromatic polymer material comprises greater than 50 and preferably greater than 70 weight percent alkenyl aromatic monomeric units. Most preferably, the alkenyl aromatic polymer material is comprised entirely of alkenyl aromatic monomeric units.
Suitable alkenyl aromatic polymers include homopolymers and copolymers derived from alkenyl aromatic compounds such as styrene, alphamethylstyrene, ethylstyrene, vinyl benzene, vinyl toluene, chlorostyrene, and bromostyrene. A preferred alkenyl aromatic polymer is polystyrene. Minor amounts of monoethylenically unsaturated compounds such as C2-6 alkyl acids and esters, ionomeric derivatives, and C4-6 dienes may be copolymerized with alkenyl aromatic compounds. Examples of copolymerizable compounds include acrylic acid, methacrylic acid, ethacrylic acid, maleic acid, itaconic acid, acrylonitrile, maleic anhydride, methyl acrylate, ethyl acrylate, isobutyl acrylate, n-butyl acrylate, methyl methacrylate, vinyl acetate and butadiene.
The term xe2x80x9csubstantially randomxe2x80x9d (in the substantially random interpolymer comprising polymer units derived from ethylene and one or more xcex1-olefin monomers with one or more vinyl or vinylidene aromatic monomers and/or aliphatic or cycloaliphatic vinyl or vinylidene monomers) as used herein means that the distribution of the monomers of said interpolymer can be described by the Bernoulli statistical model or by a first or second order Markovian statistical model, as described by J. C. Randall in POLYMER SEQUENCE DETERMINATION Carbon-13 NMR Method, Academic Press New York, 1977, pp. 71-78. Preferably, substantially random interpolymers do not contain more than 15 percent of the total amount of vinyl aromatic monomer in blocks of vinyl aromatic monomer of more than 3 units. More preferably, the interpolymer is not characterized by a high degree of either isotacticity or syndiotacticity. This means that in the carbonxe2x88x9213 NMR spectrum of the substantially random interpolymer the peak areas corresponding to the main chain methylene and methine carbons representing either meso diad sequences or racemic diad sequences should not exceed 75 percent of the total peak area of the main chain methylene and methine carbons.
The interpolymers used to prepare the foams of the present invention include the substantially random interpolymers prepared by polymerizing i) ethylene and/or one or more xcex1-olefin monomers and ii) one or more vinyl or vinylidene aromatic monomers and/or one or more sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers, and optionally iii) other polymerizable ethylenically unsaturated monomer(s). Suitable xcex1-olefins include for example, xcex1-olefins containing from 3 to about 20, preferably from 3 to about 12, more preferably from 3 to about 8 carbon atoms. Particularly suitable are ethylene, propylene, butene-1, 4-methyl-1-pentene, hexene-1 or octene-1 or ethylene in combination with one or more of propylene, butene- 1, 4-methyl-1-pentene, hexene- 1 or octene- 1. These xcex1-olefins do not contain an aromatic moiety.
Other optional polymerizable ethylenically unsaturated monomer(s) include norbornene and C1-10 alkyl or C6-10 aryl substituted norbornenes, with an exemplary interpolymer being ethylene/styrene/norbornene.
Suitable vinyl or vinylidene aromatic monomers which can be employed to prepare the interpolymers include, for example, those represented by the following formula: 
wherein R1 is selected from the group of radicals consisting of hydrogen and alkyl radicals containing from 1 to about 4 carbon atoms, preferably hydrogen or methyl; each R2 is independently selected from the group of radicals consisting of hydrogen and alkyl radicals containing from 1 to about 4 carbon atoms, preferably hydrogen or methyl; Ar is a phenyl group or a phenyl group substituted with from 1 to 5 substituents selected from the group consisting of halo, C1-4-alkyl, and C1-4-haloalkyl; and n has a value from zero to about 4, preferably from zero to 2, most preferably zero. Exemplary vinyl aromatic monomers include styrene, vinyl toluene, xcex1-methylstyrene, t-butyl styrene, chlorostyrene, including all isomers of these compounds, and the like. Particularly suitable such monomers include styrene and lower alkyl- or halogen-substituted derivatives thereof. Preferred monomers include styrene, xcex1-methyl styrene, the lower alkyl- (C1-C4) or phenyl-ring substituted derivatives of styrene, such as for example, ortho-, meta-, and para-methylstyrene, the ring halogenated styrenes, para-vinyl toluene or mixtures thereof, and the like. A more preferred aromatic vinyl monomer is styrene.
By the term xe2x80x9csterically hindered aliphatic or cycloaliphatic vinyl or vinylidene compoundsxe2x80x9d, it is meant addition polymerizable vinyl or vinylidene monomers corresponding to the formula: 
wherein A1 is a sterically bulky, aliphatic or cycloaliphatic substituent of up to 20 carbons, R1 is selected from the group of radicals consisting of hydrogen and alkyl radicals containing from 1 to about 4 carbon atoms, preferably hydrogen or methyl; each R2 is independently selected from the group of radicals consisting of hydrogen and alkyl radicals containing from 1 to about 4 carbon atoms, preferably hydrogen or methyl; or alternatively R1 and A1 together form a ring system. Preferred aliphatic or cycloaliphatic vinyl or vinylidene compounds are monomers in which one of the carbon atoms bearing ethylenic unsaturation is tertiary or quaternary substituted. Examples of such substituents include cyclic aliphatic groups such as cyclohexyl, cyclohexenyl, cyclooctenyl, or ring alkyl or aryl substituted derivatives thereof, tert-butyl, norbornyl, and the like. Most preferred aliphatic or cycloaliphatic vinyl or vinylidene compounds are the various isomeric vinyl- ring substituted derivatives of cyclohexene and substituted cyclohexenes, and 5-ethylidene-2-norbornene. Especially suitable are 1-, 3-, and 4-vinylcyclohexene. Simple linear non-branched xcex1-olefins including for example, xcex1-olefins containing from 3 to about 20 carbon atoms such as propylene, butene-1, 4-methyl-1 -pentene, hexene-1 or octene-1 are not examples of sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene compounds.
One method of preparation of the substantially random interpolymers includes polymerizing a mixture of polymerizable monomers in the presence of one or more metallocene or constrained geometry catalysts in combination with various cocatalysts, as described in EP-A-0,416,815 by James C. Stevens et al. and U.S. Pat. No. 5,703,187 by Francis J. Timmers, both of which are incorporated herein by reference in their entirety. Preferred operating conditions for such polymerization reactions are pressures from atmospheric up to 3000 atmospheres and temperatures from xe2x88x9230xc2x0 C. to 200xc2x0 C. Polymerizations and unreacted monomer removal at temperatures above the autopolymerization temperature of the respective monomers may result in formation of some amounts of homopolymer polymerization products resulting from free radical polymerization.
Examples of suitable catalysts and methods for preparing the substantially random interpolymers are disclosed in U.S. application Ser. No. 702,475, filed May 20, 1991 (EP-A-514,828); as well as U.S. Pat. Nos.: 5,055,438; 5,057,475; 5,096,867; 5,064,802; 5,132,380; 5,189,192; 5,321,106; 5,347,024; 5,350,723; 5,374,696; 5,399,635; 5,470,993; 5,703,187; and 5,721,185 all of which patents and applications are incorporated herein by reference.
The substantially random xcex1-olefin/vinyl aromatic interpolymers can also be prepared by the methods described in JP 07/278230 employing compounds shown by the general formula 
where Cp1 and Cp2 are cyclopentadienyl groups, indenyl groups, fluorenyl groups, or substituents of these, independently of each other; R1 and R2 are hydrogen atoms, halogen atoms, hydrocarbon groups with carbon numbers of 1-12, alkoxyl groups, or aryloxyl groups, independently of each other; M is a group IV metal, preferably Zr or Hf, most preferably Zr; and R3 is an alkylene group or silanediyl group used to cross-link Cp1 and Cp2).
The substantially random xcex1-olefin/vinyl aromatic interpolymers can also be prepared by the methods described by John G. Bradfute et al. (W. R. Grace and Co.) in WO 95/32095; by R. B. Pannell (Exxon Chemical Patents, Inc.) in WO 94/00500; and in Plastics Technology, p. 25 (September 1992), all of which are incorporated herein by reference in their entirety.
Also suitable are the substantially random interpolymers which comprise at least one xcex1-olefin/vinyl aromatic/vinyl aromatic/xcex1-olefin tetrad disclosed in U.S. application No. 08/708,869 filed Sep. 4, 1996 and WO 98/09999 both by Francis J. Timmers et al. These interpolymers contain additional signals in their carbon-13 NMR spectra with intensities greater than three times the peak to peak noise. These signals appear in the chemical shift range 43.70-44.25 ppm and 38.0-38.5 ppm. Specifically, major peaks are observed at 44.1, 43.9, and 38.2 ppm. A proton test NMR experiment indicates that the signals in the chemical shift region 43.70-44.25 ppm are methine carbons and the signals in the region 38.0-38.5 ppm are methylene carbons.
It is believed that these new signals are due to sequences involving two head-to-tail vinyl aromatic monomer insertions preceded and followed by at least one xcex1-olefin insertion, e.g. an ethylene/styrene/styrene/ethylene tetrad wherein the styrene monomer insertions of said tetrads occur exclusively in a 1,2 (head to tail) manner. It is understood by one skilled in the art that for such tetrads involving a vinyl aromatic monomer other than styrene and an xcex1-olefin other than ethylene that the ethylene/vinyl aromatic monomer/vinyl aromatic monomer/ethylene tetrad will give rise to similar carbon-13 NMR peaks but with slightly different chemical shifts.
These interpolymers can be prepared by conducting the polymerization at temperatures of from about xe2x88x9230xc2x0 C. to about 250xc2x0 C. in the presence of such catalysts as those represented by the formula 
wherein: each Cp is independently, each occurrence, a substituted cyclopentadienyl group xcfx80-bound to M; E is C or Si; M is a group IV metal, preferably Zr or Hf, most preferably Zr; each R is independently, each occurrence, H, hydrocarbyl, silahydrocarbyl, or hydrocarbylsilyl, containing up to about 30 preferably from 1 to about 20 more preferably from 1 to about 10 carbon or silicon atoms; each R1 is independently, each occurrence, H, halo, hydrocarbyl, hyrocarbyloxy, silahydrocarbyl, hydrocarbylsilyl containing up to about 30 preferably from 1 to about 20 more preferably from 1 to about 10 carbon or silicon atoms or two R1 groups together can be a C1-10 hydrocarbyl substituted 1,3-butadiene; m is 1 or 2; and optionally, but preferably in the presence of an activating cocatalyst. Particularly, suitable substituted cyclopentadienyl groups include those illustrated by the formula: 
wherein each R is independently, each occurrence, H, hydrocarbyl, silahydrocarbyl, or hydrocarbylsilyl, containing up to about 30 preferably from 1 to about 20 more preferably from 1 to about 10 carbon or silicon atoms or two R groups together form a divalent derivative of such group. Preferably, R independently each occurrence is (including where appropriate all isomers) hydrogen, methyl, ethyl, propyl, butyl, pentyl, hexyl, benzyl, phenyl or silyl or (where appropriate) two such R groups are linked together forming a fused ring system such as indenyl, fluorenyl, tetrahydroindenyl, tetrahydrofluorenyl, or octahydrofluorenyl.
Particularly preferred catalysts include, for example, racemic-(dimethylsilanediyl)-bis-(2-methyl-4-phenylindenyl) zirconium dichloride, racemic-(dimethylsilanediyl)-bis-(2-methyl-4-phenylindenyl) zirconium 1,4-diphenyl-1,3-butadiene, racemic-(dimethylsilanediyl)-bis-(2-methyl-4-phenylindenyl) zirconium di-C1-4 alkyl, racemic-(dimethylsilanediyl)-bis-(2-methyl-4-phenylindenyl) zirconium di-C1-4 alkoxide, or any combination thereof and the like.
It is also possible to use the following titanium-based constrained geometry catalysts, [N-(1,1 -dimethylethyl)-1,1 -dimethyl-1-[(1,2,3 ,4,5-xcex7)-1,5,6,7-tetrahydro-s- indacen-1-yl]silanaminato(2-)-N]titanium dimethyl; (1-indenyl)(tert-butylamido)-dimethylsilane titanium dimethyl; ((3-tert-butyl)(1,2,3,4,5-xcex7)-1-indenyl)(tert-butylamido) dimethylsilane titanium dimethyl; and ((3-iso-propyl)(1,2,3,4,5-xcex7)-1-indenyl)(tert-butyl amido)dimethylsilane titanium dimethyl, or any combination thereof and the like.
Further preparative methods for the interpolymers used in the present invention have been described in the literature. Longo and Grassi (Makromol. Chem., Volume 191, pages 2387 to 2396 [1990]) and D""Anniello et al. (Journal of Applied Polymer Science, Volume 58, pages 1701-1706 [1995]) reported the use of a catalytic system based on methylalumoxane (MAO) and cyclopentadienyltitanium trichloride (CpTiCl3) to prepare an ethylene-styrene copolymer. Xu and Lin (Polymer Preprints, Am. Chem. Soc., Div. Polym. Chem.) Volume 35, pages 686,687 [1994]) have reported copolymerization using a MgCl2/TiCl4/NdCl3/ Al(iBu)3 catalyst to give random copolymers of styrene and propylene. Lu et al (Journal of Applied Polymer Science, Volume 53, pages 1453 to 1460 [1994]) have described the copolymerization of ethylene and styrene using a TiCl4/NdCl3/MgCl2/Al(Et)3 catalyst. Sernetz and Mulhaupt, (Macromol. Chem. Phys., v. 197, pp. 1071-1083, 1997) have described the influence of polymerization conditions on the copolymerization of styrene with ethylene using Me2Si(Me4Cp)(N-tert-butyl)TiCl2/methylaluminoxane Ziegler-Natta catalysts. Copolymers of ethylene and styrene produced by bridged metallocene catalysts have been described by Arai, Toshiaki and Suzuki (Polymer Preprints, Am. Chem. Soc., Div. Polym. Chem.) Volume 38, pages 349, 350 [1997]) and in U.S. Pat. No. 5,652,315, issued to Mitsui Toatsu Chemicals, Inc. The manufacture of xcex1-olefin/vinyl aromatic monomer interpolymers such as propylene/styrene and butene/styrene are described in U.S. Pat. No. 5,244,996, issued to Mitsui Petrochemical Industries Ltd or U.S. Pat. No. 5,652,315 also issued to Mitsui Petrochemical Industries Ltd or as disclosed in DE 197 11 339 A1 to Denki Kagaku Kogyo KK. All the above methods disclosed for preparing the interpolymer component are incorporated herein by reference. The random copolymers of ethylene and styrene as disclosed in Polymer Preprints Vol 39, No. 1, March 1998 by Toru Aria et al. can also be employed as blend components for the foams of the present invention.
While preparing the substantially random interpolymer, an amount of atactic vinyl aromatic homopolymer may be formed due to homopolymerization of the vinyl aromatic monomer at elevated temperatures. The presence of vinyl aromatic homopolymer is in general not detrimental for the purposes of the present invention and can be tolerated. The vinyl aromatic homopolymer may be separated from the interpolymer, if desired, by extraction techniques such as selective precipitation from solution with a non solvent for either the interpolymer or the vinyl aromatic homopolymer. For the purpose of the present invention it is preferred that no more than 30 weight percent, preferably less than 20 weight percent based on the total weight of the interpolymers of atactic vinyl aromatic homopolymer is present.
Preparation of the Foams of the Present Invention
The compositions of the present invention may be used to form extruded thermoplastic polymer foam, expandable thermoplastic foam beads or expanded thermoplastic foams, and molded articles formed by expansion and/or coalescing and welding of those particles.
The foams may take any known physical configuration, such as extruded sheet, rod, plank, films and profiles. The foam structure also may be formed by molding expandable beads into any of the foregoing configurations or any other configuration.
Foam structures may be made by a conventional extrusion foaming process. The present foam is generally prepared by melt blending in which the alkenyl aromatic polymer material and one or more substantially random interpolymers are heated together to form a plasticized or melt polymer material, incorporating therein a blowing agent to form a foamable gel, and extruding the gel through a die to form the foam product. Prior to extruding from the die, the gel is cooled to an optimum temperature. To make a foam, the optimum temperature is at or above the blends glass transition temperature or melting point. For the foams of the present invention the optimum foaming temperature is in a range sufficient to produce an open cell content in the foam of 20 vol % or less and to optimize physical characeristics of the foam structure. The blowing agent may be incorporated or mixed into the melt polymer material by any means known in the art such as with an extruder, mixer, blender, or the like. The blowing agent is mixed with the melt polymer material at an elevated pressure sufficient to prevent substantial expansion of the melt polymer material and to generally disperse the blowing agent homogeneously therein. Optionally, a nucleator may be blended in the polymer melt or dry blended with the polymer material prior to plasticizing or melting. The substantially random interpolymers may be dry-blended with the polymer material prior to charging to the extruder, or charged to the extruder in the form of a polymer concentrate or a interpolymer/color pigment carrier material. The foamable gel is typically cooled to a lower temperature to optimize physical characteristics of the foam structure. The gel may be cooled in the extruder or other mixing device or in separate coolers. The gel is then extruded or conveyed through a die of desired shape to a zone of reduced or lower pressure to form the foam structure. The zone of lower pressure is at a pressure lower than that in which the formable gel is maintained prior to extrusion through the die. The lower pressure may be superatmospheric or subatmospheric (vacuum), but is preferably at an atmospheric level.
The present foam structures may be formed in a coalesced strand form by extrusion of the compositions of the present invention through a multi-orifice die. The orifices are arranged so that contact between adjacent streams of the molten extrudate occurs during the foaming process and the contacting surfaces adhere to one another with sufficient adhesion to result in a unitary foam structure. The streams of molten extrudate exiting the die take the form of strands or profiles, which desirably foam, coalesce, and adhere to one another to form a unitary structure. Desirably, the coalesced individual strands or profiles should remain adhered in a unitary structure to prevent strand delamination under stresses encountered in preparing, shaping, and using the foam. Apparatuses and method for producing foam structures in coalesced strand form are seen in U.S. Pat. Nos. 3,573,152 and 4,824,720, both of which are incorporated herein by reference.
The present foam structures may also be formed by an accumulating extrusion process as seen in U.S. Pat. No. 4,323,528, which is incorporated by reference herein. In this process, low density foam structures having large lateral cross-sectional areas are prepared by: 1) forming under pressure a gel of the compositions of the present invention and a blowing agent at a temperature at which the viscosity of the gel is sufficient to retain the blowing agent when the gel is allowed to expand; 2) extruding the gel into a holding zone maintained at a temperature and pressure which does not allow the gel to foam, the holding zone having an outlet die defining an orifice opening into a zone of lower pressure at which the gel foams, and an openable gate closing the die orifice; 3) periodically opening the gate; 4) substantially concurrently applying mechanical pressure by a movable ram on the gel to eject it from the holding zone through the die orifice into the zone of lower pressure, at a rate greater than that at which substantial foaming in the die orifice occurs and less than that at which substantial irregularities in cross-sectional area or shape occurs; and 5) permitting the ejected gel to expand unrestrained in at least one dimension to produce the foam structure.
The present foam structures may also be formed into foam beads suitable for molding into articles by expansion of pre-expanded beads containing a blowing agent. The beads may be molded at the time of expansion to form articles of various shapes. Processes for making expanded beads and molded expanded beam foam articles are described in Plastic Foams, Part II, Frisch And Saunders, pp. 544-585, Marcel Dekker, Inc. (1973) and Plastic Materials, Brydson, 5th Ed., pp. 426-429, Butterworths (1989).
Expandable and expanded beads can be made by a batch or by an extrusion process. The batch process of making expandable beads is essentially the same as for manufacturing expandable polystyrene (EPS). The granules of a polymer blend, made either by melt blending or in-reactor blending, are impregnated with a blowing agent in an aqueous suspension or in an anhydrous state in a pressure vessel at an elevated temperature and pressure. The granules are then either rapidly discharged into a region of reduced pressure to expand to foam beads or cooled and discharged as unexpanded beads. The unexpanded beads are then heated to expand with a proper means, e.g., with steam or with hot air. The extrusion method is essentially the same as the conventional foam extrusion process as described above up to the die orifice. The die has multiple holes. In order to make unfoamed beads, the foamable strands exiting the die orifice are immediately quenched in a cold water bath to prevent foaming and then pelletized. Or, the strands are converted to foam beads by cutting at the die face and then allowed to expand.
The foam beads may then be molded by any means known in the art, such as charging the foam beads to the mold, compressing the mold to compress the beads, and heating the beads such as with steam to effect coalescing and welding of the beads to form the article. Optionally, the beads may be impregnated with air or other blowing agent at an elevated pressure and temperature prior to charging to the mold. Further, the beads may be heated prior to charging. The foam beads may then be molded to blocks or shaped articles by a suitable molding method known in the art. (Some of the methods are taught in U.S. Pat. Nos. 3,504,068 and 3,953,558.) Excellent teachings of the above processes and molding methods are seen in C.P. Park, supra, p. 191, pp. 197-198, and pp. 227-229, which are incorporated herein by reference.
To make the foam beads, blends of alkenyl aromatic polymers with one or more substantially random interpolymer are formed into discrete resin particles such as granulated resin pellets and are: suspended in a liquid medium in which they are substantially insoluble such as water; impregnated with a blowing agent by introducing the blowing agent into the liquid medium at an elevated pressure and temperature in an autoclave or other pressure vessel; and rapidly discharged into the atmosphere or a region of reduced pressure to expand to form the foam beads. This process is well taught in U.S. Pat. Nos. 4,379,859 and 4,464,484, which are incorporated herein by reference.
A process for making expandable thermoplastic beads comprises: providing an alkenyl aromatic monomer and optionally at least one additional monomer, which is different from, and polymerizable with said alkenyl aromatic monomer; and dissolving in at least one of said monomers the substantially random interpolymers; polymerizing the first and second monomers to form thermoplastic particles; incorporating a blowing agent into the thermoplastic particles during or after polymerization; and cooling the thermoplastic particles to form expandable beads. The alkenyl aromatic monomer is present in an amount of at least about 50, preferably at least about 70, more preferably at least about 90 wt % based on the combined weights of the polymerizeable monomer(s).
Another process for making expandable thermoplastic beads comprises: heating the blends of alkenyl aromatic polymers with one or more substantially random interpolymers to form a melt polymer; incorporating into the melt polymer material at an elevated temperature a blowing agent to form a foamable gel; cooling the gel to an optimum temperature which is one at which foaming will not occur, extruding through a die containing one or more orifices to form one or more essentially continuous expandable thermoplastic strand(s); and pelletizing the expandable thermoplastic strand(s) to form expandable thermoplastic bead(s). Alternatively expanded thermoplastic foam beads may be made if, prior to extruding from the die, the gel is cooled to an optimum temperature which in this case is at or above the blends glass transition temperature or melting point. For the expanded thermoplastic foam beads of the present invention, the optimum foaming temperature is in a range sufficient to produce an open cell content in the foam of 20 vol % or less.
The present foam structures may also be used to make foamed films for bottle labels and other containers using either a blown film or a cast film extrusion process. The films may also be made by a co-extrusion process to obtain foam in the core with one or two surface layers, which may or may not be comprised of the polymer compositions used in the present invention.
Due to present environmental concerns over the use of potentially ozone-depleting blowing agents, it is desirable to make alkenyl aromatic polymer foams with blowing agents having reduced or zero ozone-depletion potential. Such blowing agents include inorganic blowing agents such as nitrogen, sulfur hexafluoride (SF6), and argon; organic blowing agents such as carbon dioxide and hydrofluorocarbons such as 1,1,1,2-tetrafluoroethane (HFC-134a), difluoromethane (HFC-32), 1,1-difluoroethane (HFC-152a), 1,1,2,2-tetrafluoroethane (HFC-134), 1,1,1,3,3-pentafluoropropane, pentafluoroethane (HFC-125), fluoroethane (HFC-161) and 1,1,1 -trifluoroethane (HFC-143a) and hydrocarbons such as methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane, cyclopentane and neopentane; and chemical blowing agents which include azodicarbonamide, azodiisobutyro-nitrile, benzenesulfonhydrazide, 4,4-oxybenzene sulfonyl-semicarbazide, p-toluene sulfonyl semi-carbazide, barium azodicarboxylate, N,Nxe2x80x2-dimethyl-N,Nxe2x80x2-dinitroso-terephthalamide, trihydrazino triazine and mixtures of citric acid and sodium bicarbonate such as the various products sold under the name Hydrocerol(trademark) ( a product and trademark of Boehringer Ingelheim). All of these blowing agents may be used as single components or any mixture of combination thereof, or in mixtures with other co-blowing agents.
The blowing agent(s), when mixed with a co-blowing agent, are present in an amount of 50 mole % or more, preferably 70 mole % or more (based on the total g-moles of blowing agent and co-blowing agent).
Co-blowing agents useful with the blowing agents used in the present invention include inorganic co-blowing agents, organic co-blowing agents and chemical co-blowing agents. Suitable inorganic co-blowing agents include helium, water and air. Organic co-blowing agents include aliphatic alcohols including methanol, ethanol, n-propanol, and isopropanol. Fully and partially halogenated aliphatic hydrocarbons include fluorocarbons, chlorocarbons, and chlorofluorocarbons. Examples of fluorocarbons include methyl fluoride, perfluoromethane, ethyl fluoride, perfluoroethane, 2,2-difluoropropane, 1,1,1 -trifluoropropane, perfluoropropane, dichloropropane, difluoropropane, perfluorobutane, perfluorocyclobutane. Partially halogenated chlorocarbons and chlorofluorocarbons for use in this invention include methyl chloride, methylene chloride, ethyl chloride, 1,1,1 -trichloro-ethane, 1,1-dichloro-1-fluoroethane (HCFC-141b), 1-chloro-1,1-difluoroethane (HCFC-142b), chlorodifluoromethane (HCFC-22), 1,1 -dichloro-2,2,2-trifluoroethane (HCFC- 123) and 1-chloro-1,2,2,2-tetrafluoroethane (HCFC-124). Fully halogenated chlorofluorocarbons include trichloromonofluoromethane (CFC-1 1), dichlorodifluoromethane (CFC-12), trichloro-trifluoroethane (CFC-113), dichlorotetrafluoroethane (CFC-114), chloroheptafluoropropane, and dichlorohexafluoropropane.
The total amount of blowing agents and co-blowing agents incorporated into the polymer melt material to make a foam-forming polymer gel is from about 0.2 to about 5.0 gram-moles per kilogram of polymer, preferably from about 0.5 to about 3.0 gram-moles per kilogram of polymer, and most preferably from about 1.0 to 2.5 gram-moles per kilogram of polymer.
In addition, a nucleating agent may be added in order to control the size of foam cells. Preferred nucleating agents include inorganic substances such as calcium carbonate, talc, clay, silica, barium stearate, diatomaceous earth, mixtures of citric acid and sodium bicarbonate, and the like. The amount of nucleating agent employed may range from 0 to about 5 parts by weight per hundred parts by weight of a polymer resin. The preferred range is from 0 to about 3 parts by weight.
Various additives may be incorporated in the present foam structure such as inorganic fillers, pigments, antioxidants, acid scavengers, ultraviolet absorbers, flame retardants, processing aids, extrusion aids, other thermoplastic polymers, antistatic agents, and the like. Examples of other thermoplastic polymers include alkenyl aromatic homopolymers or copolymers (having molecular weight of about 2,000 to about 50,000) and ethylenic polymers.
The foam has a density of from about 10 to about 150 and most preferably from about 10 to about 70 kilograms per cubic meter according to ASTM D-1622-88. The foam has an average cell size of from about 0.05 to about 5.0 and preferably from about 0.1 to about 1.5 millimeters according to ASTM D3576-77.
The present foam has an increase of cell size of about 5%, preferably about 10%, more preferably about 15% or more relative to an analogous foam made without the substantially random interpolymer.
The present foam is particularly suited to be formed into a plank or sheet, desirably one having a cross-sectional area of 30 square centimeters (cm) or more and a thickness or minor dimension in cross-section of 0.95 cm or more, preferably 2.5 cm or more.
The present foam is closed cell. The closed cell content of the present foams is greater than or equal to 80 percent according to ASTM D2856-94.
The present foam structures may be used to insulate a surface by applying to the surface an insulating panel fashioned from the present structure, as used in for example, external wall sheathing (home thermal insulation), foundation insulation, and residing underlayment. Such panels are useful in any conventional insulating applications such as roofing, buildings, refrigerators and the like. Other applications include floating docks and rafts (buoyancy applications) as well as various floral and craft applications.
Properties of the Interpolymers and Blend Compositions Used to Prepare the Foams of the Present Invention
The polymer compositions used to prepare the foams of the present invention comprise from about 80 to about 99.7, preferably from about 80 to about 99.5, more preferably from about 80 to about 99 wt %, (based on the combined weights of substantially random interpolymer and the alkenyl aromatic homopolymers or copolymer) of one or more alkenyl aromatic homopolymers or copolymers.
The molecular weight distribution (Mw/Mn) of the alkenyl aromatic homopolymers or copolymers used to prepare the foams having enlarged cell size of the present invention is from about 2 to about 7.
The molecular weight (Mw) of the alkenyl aromatic homopolymers or copolymers used to prepare the foams having enlarged cell size of the present invention is from about 100,000 to about 500,000, preferably from about 120,000 to about 350,000, more preferably 130,000 to 325,000.
The alkenyl aromatic polymer material used to prepare the foams of the present invention comprises greater than 50 and preferably greater than 70 weight percent alkenyl aromatic monomeric units. Most preferably, the alkenyl aromatic polymer material is comprised entirely of alkenyl aromatic monomeric units.
The polymer compositions used to prepare the foams of the present invention comprise from about 0.3 to about 20, preferably from about 0.5 to about 20, more preferably from about 1 to about 20 wt %, (based on the combined weights of substantially random interpolymer and the alkenyl aromatic homopolymers or copolymers) of one or more substantially random interpolymers.
These substantially random interpolymers used to prepare the foams having enlarged cell size of the present invention usually contain from about 8 to about 65, preferably from about 10 to about 45, more preferably from about 13 to about 39 mole percent of at least one vinyl or vinylidene aromatic monomer and/or aliphatic or cycloaliphatic vinyl or vinylidene monomer and from about 35 to about 92, preferably from about 55 to about 90, more preferably from about 61 to about 87 mole percent of ethylene and/or at least one aliphatic xcex1-olefin having from 3 to about 20 carbon atoms.
The melt index (I2) of the substantially random interpolymers used to prepare the foams of the present invention is from about 0.01 to about 1000, preferably of from about 0.3 to about 30, more preferably of from about 0.5 to about 10 g/10 min.
The molecular weight distribution (Mw/Mn) of the substantially random interpolymer used to prepare the foams having enlarged cell size of the present invention is from about 1.5 to about 20, preferably of from about 1.8 to about 10, more preferably of from about 2 to about 5.
In addition, minor amounts of alkenyl aromatic homopolymers or copolymers having a molecular weight of about 2,000 to about 50,000, preferably from about 4,000 to about 25,000 can be added in an amount not exceeding about 20 wt % (based on the combined weights of substantially random interpolymer and the various alkenyl aromatic homopolymers or copolymers).